Installing an operating system on the 11/83 - update.

DD 5.25" disks are about 300 Oersted. HD 5.25" disks are about 600 Oersted. If you use HD disks to write DD content, the data fades away real fast. However, on 3.5" disks, the difference is more like 600 Oersted VS 750 Oersted, and you may get away with using the wrong disk. 360K disks are tested/certified for 40 track (48tpi) double density. Although not tested/certified for 80 track 96tpi, the cookie is the same, and they generally can handle 80 track (96tp) double density just fine. Disks of extremely marginal quality (such as Wabash, or pre-Datalife Verbatem) can still give you troubles. In general, commercial 1.2M drives are also intended to be able to read/write(with track width problems!) 360K disks. So, if the write current is at the "360K" level, and you get the data transfer rate correct (250K at 300RPM or 300K at 360RPM), and you get the drive to NOT "double step", then you can, indeed, read/write 80 track DD disks using a 1.2M drive. Using a double density 80 track drive, such as the the Tandon TM100-4, Shugart/Panasonic/Matsushita 465, or the Teac 55F makes it a little simpler/easier, since those drives don't HAVE multiple write currents, nor 360RPM, so just let the PC FDC think that it is a 360K drive (other than being 96tpi with 80 tracks), and the other issues aren't there. 10 512 byte sectors per track is similar to the 8 or 9 sector per track PC track format, other than squeezing an extra sector onto each track, by redducing the sector gaps. Readily doable with INT13h (plus INT 1Eh), and not even having to talk directly to the FDC. -- Grumpy Ol' Fred cisin at xenosoft.com On Wed, 23 Feb 2022, Ray Jewhurst via cctalk wrote: